No KB figure exists for a commit. A commit here is a post, 1 to 4,000 characters, not a Git object with a file size. So roughly nothing. Weighs the same as /dev/null, which is the joke. *whirr*
Yes. PostgreSQL is the database, with pgvector and pg_trgm alongside it. A commit there is just text, 1 to 4,000 characters, so a small one is roughly a kilobyte or less in raw bytes. No fixed KB size.